The relatively low coefficient of thermal expansion of cordierite makes its use advantageous in various types of ceramic bodies. Ceramics containing cordierite crystals (2MgO.2Al.sub.2 O.sub.3.5SiO.sub.2, corresponding to an oxide composition of 51.3% SiO.sub.2, 34.9% Al.sub.2 O.sub.3, and 13.8% MgO) are well known, and have coefficients of thermal expansion ("TEC") in the range of approximately 14-40.times.10.sup.-7 /.degree.C.
Its advantageous low expansion notwithstanding, cordierite has found only limited use in "whiteware" ceramics, that is, ceramics for cooking and dining use. One reason for this has been the difficulty of achieving sufficiently high strength and thermal shock resistance for whiteware use. Secondly, such ceramics have been of limited glazability, generally requiring Li.sub.2 O-containing glazes which are highly crystalline.
A modulus of rupture ("MOR") strength of at least 12,000 psi is needed for adequate durability in commercial (e.g., restaurant or hotel) use. The difficulty in achieving such high strength arises at least in part from the relatively high porosities which characterize most cordierite ceramics. In the sintering reaction which creates the cordierite crystals, only a small proportion of non-crystalline (glassy) binder phase can form without deformation of the ware. Because of the low proportion of glass, the voids between the crystals are not well sealed and the body remains relatively porous. As a general rule, strength (in terms of modulus of rupture) decreases as porosity increases. Thus low porosity is requisite to obtaining adequate strength.
In order to reduce porosity, it is known to include a flux such as nepheline syenite and/or feldspar in the batch composition. However, if such fluxing agents are included, the resulting composition often must be fired under special and restrictive conditions, at high rate of temperature increase (e.g., at least 4.degree. C./min. in the higher temperature range) or to a maturing or peak temperature which is within narrow limits (e.g., 1250.degree..+-.10.degree. C.), for the resulting fired ceramic body to display the desired properties. It has therefore been desirable to provide a ceramic which can be fired at either a low or a high rate of temperature increase (including the rate of a conventional low rate kiln), and in which peak temperature range is not so narrowly restricted.